On Fri, Jul 26, 2024 at 07:28:28PM +0100, David Woodhouse wrote: > On 26 July 2024 17:49:58 BST, Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> wrote: > >On Thu, 25 Jul 2024 14:50:50 +0100 > >David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote: > > > >> On Thu, 2024-07-25 at 08:33 -0400, Michael S. Tsirkin wrote: > >> > On Thu, Jul 25, 2024 at 01:31:19PM +0100, David Woodhouse wrote: > >> > > On Thu, 2024-07-25 at 08:29 -0400, Michael S. Tsirkin wrote: > >> > > > On Thu, Jul 25, 2024 at 01:27:49PM +0100, David Woodhouse wrote: > >> > > > > On Thu, 2024-07-25 at 08:17 -0400, Michael S. Tsirkin wrote: > >> > > > > > On Thu, Jul 25, 2024 at 10:56:05AM +0100, David Woodhouse wrote: > >> > > > > > > > Do you want to just help complete virtio-rtc then? Would be easier than > >> > > > > > > > trying to keep two specs in sync. > >> > > > > > > > >> > > > > > > The ACPI version is much more lightweight and doesn't take up a > >> > > > > > > valuable PCI slot#. (I know, you can do virtio without PCI but that's > >> > > > > > > complex in other ways). > >> > > > > > > > >> > > > > > > >> > > > > > Hmm, should we support virtio over ACPI? Just asking. > >> > > > > > >> > > > > Given that we support virtio DT bindings, and the ACPI "PRP0001" device > >> > > > > exists with a DSM method which literally returns DT properties, > >> > > > > including such properties as "compatible=virtio,mmio" ... do we > >> > > > > already? > >> > > > > > >> > > > > > >> > > > > >> > > > In a sense, but you are saying that is too complex? > >> > > > Can you elaborate? > >> > > > >> > > No, I think it's fine. I encourage the use of the PRP0001 device to > >> > > expose DT devices through ACPI. I was just reminding you of its > >> > > existence. > >> > > >> > Confused. You said "I know, you can do virtio without PCI but that's > >> > complex in other ways" as the explanation why you are doing a custom > >> > protocol. > >> > >> Ah, apologies, I wasn't thinking that far back in the conversation. > >> > >> If we wanted to support virtio over ACPI, I think PRP0001 can be made > >> to work and isn't too complex (even though it probably doesn't yet work > >> out of the box). > >> > >> But for the VMCLOCK thing, yes, the simple ACPI device is a lot simpler > >> than virtio-rtc and much more attractive. > >> > >> Even if the virtio-rtc specification were official today, and I was > >> able to expose it via PCI, I probably wouldn't do it that way. There's > >> just far more in virtio-rtc than we need; the simple shared memory > >> region is perfectly sufficient for most needs, and especially ours. > >> > >> I have reworked > >> https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/vmclock > >> to take your other feedback into account. > >> > >> It's now more flexible about the size handling, and explicitly checking > >> that specific fields are present before using them. > >> > >> I think I'm going to add a method on the ACPI device to enable the > >> precise clock information. I haven't done that in the driver yet; it > >> still just consumes the precise clock information if it happens to be > >> present already. The enable method can be added in a compatible fashion > >> (the failure mode is that guests which don't invoke this method when > >> the hypervisor needs them to will see only the disruption signal and > >> not precise time). > >> > >> For the HID I'm going to use AMZNVCLK. I had used QEMUVCLK in the QEMU > >> patches, but I'll change that to use AMZNVCLK too when I repost the > >> QEMU patch. > > > >That doesn't fit with ACPI _HID definitions. > >Second set 4 characters need to be hex digits as this is an > >ACPI style ID (which I assume this is given AMZN is a valid > >vendor ID. 6.1.5 in ACPI v6.5 > > > >Maybe I'm missing something... > > > >J > > > > > > > > Hm, is the same not true for QEMUVGID and AMZNVGID, which I was using as an example? > > QEMU seemed to get to 0002, and AFAICT the VMGENID patches were initially posted using QEMU0003, but what's actually in QEMU now is QEMUVGID. So I presumed that was now the preferred option. Glad you asked :) ACPI 1.0 indeed did not place restrictions on it: 6.1.4 _HID This object is used to supply the OS with the device’s Plug and Play Hardware ID. When describing a platform, use of any _HID objects is optional. However, a _HID object must be used to describe any device that will be enumerated by the ACPI driver. The ACPI driver only enumerates a device when no bus enumerator can detect the device ID. For example, devices on an ISA bus are enumerated by the ACPI driver. Use the _ADR object to describe devices enumerated by bus enumerators other than the ACPI driver. A _HID object evaluates to either a numeric 32-bit compressed EISA type ID or a string. Then 3.0 was very draconic: 6.1.4 _HID (Hardware ID) This object is used to supply OSPM with the device’s Plug and Play hardware ID.8 When describing a platform, use of any _HID objects is optional. However, a _HID object must be used to describe any device that will be enumerated by OSPM. OSPM only enumerates a device when no bus enumerator can detect the device ID. For example, devices on an ISA bus are enumerated by OSPM. Use the _ADR object to describe devices enumerated by bus enumerators other than OSPM. A _HID object evaluates to either a numeric 32-bit compressed EISA type ID or a string. If a string, the format must be an alphanumeric PNP or ACPI ID with no asterisk or other leading characters. A valid PNP ID must be of the form “AAA####” where A is an uppercase letter and # is a hex digit. A valid ACPI ID must be of the form “ACPI####” where # is a hex digit. Then 5.0 changed it to: 6.1.5 _HID (Hardware ID) This object is used to supply OSPM with the device’s Plug and Play hardware ID.1 1. 256 A Plug and Play ID or ACPI ID can be obtained by sending e-mail to pnpid@xxxxxxxxxxxxx. Hewlett-Packard/Intel/Microsoft/Phoenix/ToshibaAdvanced Configuration and Power Interface Specification When describing a platform, use of any _HID objects is optional. However, a _HID object must be used to describe any device that will be enumerated by OSPM. OSPM only enumerates a device when no bus enumerator can detect the device ID. For example, devices on an ISA bus are enumerated by OSPM. Use the _ADR object to describe devices enumerated by bus enumerators other than OSPM. Arguments: None Return Value: An Integer or String containing the HID A _HID object evaluates to either a numeric 32-bit compressed EISA type ID or a string. If a string, the format must be an alphanumeric PNP or ACPI ID with no asterisk or other leading characters. A valid PNP ID must be of the form "AAA####" where A is an uppercase letter and # is a hex digit. A valid ACPI ID must be of the form "NNNN####" where N is an uppercase letter or a digit ('0'-'9') and # is a hex digit. This specification reserves the string "ACPI" for use only with devices defined herein. It further reserves all strings representing 4 HEX digits for exclusive use with PCI-assigned Vendor IDs. Long story short, QEMUVGID is indeed out of spec, but it works both because of guest compatibility with ACPI 1.0, and because no one much uses it. -- MST
